UPSTREAM: arm64: mm: Add arm64_kernel_unmapped_at_el0 helper

In order for code such as TLB invalidation to operate efficiently when
the decision to map the kernel at EL0 is determined at runtime, this
patch introduces a helper function, arm64_kernel_unmapped_at_el0, to
determine whether or not the kernel is mapped whilst running in userspace.

Currently, this just reports the value of CONFIG_UNMAP_KERNEL_AT_EL0,
but will later be hooked up to a fake CPU capability using a static key.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit fc0e1299da)

Change-Id: I2d34c2d7b88f82d848d7063efdae7c3cc4fe8fd6
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

arch/arm64/include/asm/mmu.h

@@ -19,6 +19,8 @@
 
 #define USER_ASID_FLAG	(UL(1) << 48)
 
+#ifndef __ASSEMBLY__
+
 typedef struct {
 	atomic64_t	id;
 	void		*vdso;
@@ -31,6 +33,11 @@ typedef struct {
  */
 #define ASID(mm)	((mm)->context.id.counter & 0xffff)
 
+static inline bool arm64_kernel_unmapped_at_el0(void)
+{
+	return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0);
+}
+
 extern void paging_init(void);
 extern void bootmem_init(void);
 extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
@@ -40,4 +47,5 @@ extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 			       pgprot_t prot, bool allow_block_mappings);
 extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
 
+#endif	/* !__ASSEMBLY__ */
 #endif